This invention relates to an electric circuit which provides protection to a power source supplying power to a load through a resonant circuit. In such ciruits a cyclical operation takes place in which a direct current power supply charges a capacitor and the power stored in the capacitor is then discharged through the load. The discharge supplies operating power to the load and the present invention applies in particular to a load which needs repetitive discharges over an extended period or for continuous operation.
In such circuits the discharge of the capacitor through the load can be initiated by a switch device which connects the fully-charged capacitor across the load. At the appropriate time it is necessary for the switch device to become open circuit so that the capacitor can recharge and the regular operation of the circuit requires that this should occur.
If the switch device fails to become open circuit it effectively presents a short circuit to the power supply and unless the switch becomes open circuit within a predetermined time, the protective circuits of the power supply will cause the power supply to switch off to prevent it being damaged. The present invention provides a protective circuit to prevent just such an occurrence.